Conventional finned heat exchanger panels, by virtue of their fins, increase the available heat-exchanging surface several-fold, but most of the increase is secondary, out-of-direct contact with the heat exchange fluid passing through. The capacity of these panels is usually limited to a heat exchange coefficient K in the range of 1.1 BTU per sq. ft. of surface times the difference in temperature between the heat exchanger and the surrounding air.
Prior art heat exchanger panels also have the inherent disadvantages of tending to become fouled outside with use, and are difficult to clean because of the many sharp edges and corners characteristic of secondary finned surface.